From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-12.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 74F6EC04EB9 for ; Thu, 29 Nov 2018 21:55:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3EC7E2145D for ; Thu, 29 Nov 2018 21:55:26 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3EC7E2145D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726685AbeK3JCQ (ORCPT ); Fri, 30 Nov 2018 04:02:16 -0500 Received: from mx1.redhat.com ([209.132.183.28]:24937 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726381AbeK3JCP (ORCPT ); Fri, 30 Nov 2018 04:02:15 -0500 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 6A5EC4E928; Thu, 29 Nov 2018 21:55:23 +0000 (UTC) Received: from dustball.brq.redhat.com (unknown [10.43.17.9]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0BD1E601B9; Thu, 29 Nov 2018 21:55:17 +0000 (UTC) From: Jan Stancek To: linux-mm@kvack.org, lersek@redhat.com, alex.williamson@redhat.com, aarcange@redhat.com, rientjes@google.com, kirill@shutemov.name, mgorman@techsingularity.net, mhocko@suse.com, jstancek@redhat.com Cc: linux-kernel@vger.kernel.org Subject: [PATCH] mm: page_mapped: don't assume compound page is huge or THP Date: Thu, 29 Nov 2018 22:53:48 +0100 Message-Id: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Thu, 29 Nov 2018 21:55:23 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org LTP proc01 testcase has been observed to rarely trigger crashes on arm64: page_mapped+0x78/0xb4 stable_page_flags+0x27c/0x338 kpageflags_read+0xfc/0x164 proc_reg_read+0x7c/0xb8 __vfs_read+0x58/0x178 vfs_read+0x90/0x14c SyS_read+0x60/0xc0 Issue is that page_mapped() assumes that if compound page is not huge, then it must be THP. But if this is 'normal' compound page (COMPOUND_PAGE_DTOR), then following loop can keep running until it tries to read from memory that isn't mapped and triggers a panic: for (i = 0; i < hpage_nr_pages(page); i++) { if (atomic_read(&page[i]._mapcount) >= 0) return true; } I could replicate this on x86 (v4.20-rc4-98-g60b548237fed) only with a custom kernel module [1] which: - allocates compound page (PAGEC) of order 1 - allocates 2 normal pages (COPY), which are initialized to 0xff (to satisfy _mapcount >= 0) - 2 PAGEC page structs are copied to address of first COPY page - second page of COPY is marked as not present - call to page_mapped(COPY) now triggers fault on access to 2nd COPY page at offset 0x30 (_mapcount) [1] https://github.com/jstancek/reproducers/blob/master/kernel/page_mapped_crash/repro.c This patch modifies page_mapped() to check for 'normal' compound pages (COMPOUND_PAGE_DTOR). Debugged-by: Laszlo Ersek Signed-off-by: Jan Stancek --- include/linux/mm.h | 9 +++++++++ mm/util.c | 2 ++ 2 files changed, 11 insertions(+) diff --git a/include/linux/mm.h b/include/linux/mm.h index 5411de93a363..18b0bb953f92 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -700,6 +700,15 @@ static inline compound_page_dtor *get_compound_page_dtor(struct page *page) return compound_page_dtors[page[1].compound_dtor]; } +static inline int PageNormalCompound(struct page *page) +{ + if (!PageCompound(page)) + return 0; + + page = compound_head(page); + return page[1].compound_dtor == COMPOUND_PAGE_DTOR; +} + static inline unsigned int compound_order(struct page *page) { if (!PageHead(page)) diff --git a/mm/util.c b/mm/util.c index 8bf08b5b5760..06c1640cb7b3 100644 --- a/mm/util.c +++ b/mm/util.c @@ -478,6 +478,8 @@ bool page_mapped(struct page *page) return true; if (PageHuge(page)) return false; + if (PageNormalCompound(page)) + return false; for (i = 0; i < hpage_nr_pages(page); i++) { if (atomic_read(&page[i]._mapcount) >= 0) return true; -- 1.8.3.1